The decarboxylation of ornithine to putrescine, a reaction catalyzed by the enzyme ornithine decarboxylase (ODC), is the first step in the biosynthesis of the polyamines spermidine and spermine. Spermidine is formed by the transfer of an activated aminopropyl moiety from S-adenosyl S-methyl homocysteamine to putrescine, while spermine is formed by the transfer of a second aminopropyl group to spermidine. S-Adenosyl S-methyl homocysteamine is formed by the decarboxylation of S-adenosylmethionine (SAM), a reaction catalyzed by the enzyme S-adenosylmethionine decarboxylase (SAM-DC).
The polyamines, which are found in animal tissues and microorganisms, are known to play an important role in cell growth and proliferation. The onset of cell growth and proliferation is associated with both a marked increase in ODC activity and an increase in the levels of putrescine and the polyamines. Although the exact mechanism of the role of the polyamines in cell growth and proliferation is not known, it appears that the polyamines may facilitate macromolecular processes such as DNA, RNA, or protein synthesis. Polyamine levels are known to be high in embryonic tissue; in the testes, ventral prostrate, and thymus; in tumor tissue; in psoriatic skin lesions; and in other cells undergoing rapid growth or proliferation.
Since putrescine is the precursor of both spermidine and spermine, blockade of the conversion of ornithine to putrescine, such as by inhibition of ODC, should prevent new biosynthesis of these polyamines and, thus, provide beneficial physiological effects.
We have disclosed in U.S. Pat. No. 4,139,563 that inter alia compounds of the following Formula A are inhibitors of ornithine decarboxylase: ##STR2## wherein R represents hydrogen or C.sub.1 -C.sub.4 alkyl.
Further, we have disclosed in U.S. Pat. No. 4,421,768 that compounds of the following Formula B also are ornithine decarboxylase inhibitors: ##STR3## wherein p represents 1 or 2.